A manufacturing apparatus for the production of cosmetics such as cream and emulsion, emulsified foods, paints and the like dispersions is known having (1) a vacuum emulsifier, (2) an open emulsifier and (3) a continuously stirring and kneading reaction heat exchanger (the so-called mixing reactor or scraped surface heat exchangers).
The emulsifier effectuates stirring and emulsification under vacuum in a confined state. The emulsification is carried out under vacuum so that the emulsifier is suitable for the manufacture of sterilized products and aerial bubble-free products.
The open emulsifier has been used for some time. In this open emulsifier, aerial bubbles tend to enter on emulsification and evaporation of water and the like occurs during stirring for emulsification at a high temperature. In general, evaporation of an amount of about 2-5% based on the amount charged occurs, although it varies according to the recipe and the amount for batch. Further, careful attention should be paid to the heating temperature, heating time, stirring speed and the like. A cream manufactured by the open emulsifier contains about 2-10% by weight of aerial bubbles as compared with a cream manufactured by a vacuum emulsifier. In case the resultant cream is charged into a bottle or the like container, therefore, the amount to be charged will be decreased by the amount corresponding to the aerial bubbles.
The following points are mentioned as problems existing commonly in the above described vacuum and open emulsifiers:
.circle.1 On account of a batchwise system, an emulsifying tank will inevitably become larger so that it takes much time to charge the tank with materials and to discharge the emulsion from the tank,thus making the system inefficient.
.circle.2 As the emulsifying tank is larger, little turbulence occurs and dead spaces also tend to be formed. Accordingly, cutting of particles with blades of a propeller hardly tends to be effected completely and evenly so that an entire emulsion will hardly be formed even after the lapse of a sufficient time.
.circle.3 As the emulsifying tank is larger, it is difficult to obtain the number of revolutions necessary for cutting particles (desirably at least 6,000 r.p.m.). However, only about 3,000 r.p.m. is obtained with a drive having power as high as 7 horse power or more for a tank with a capacity of 300 liters and a drive as high as 15 horse power or more for a tank with a capacity of 1,000 liters, thus making the operation uneconomical.
.circle.4 As the apparatus is large, a number of employees are required for the operations. Moreover, a lot of cost is required if the apparatus is additionally installed.
.circle.5 On account of a batchwise system, much time is necessary for the production of an emulsion and a warmth-maintaining device is required in some cases, thus making the operation uneconomical.
A substantial structure is required for the continuously stirring and kneading reaction heat exchanger as discussed above wherein starting materials dissolved in a starting materials-dissolving tank are emulsified in a preliminary emulsifying tank and the preliminarily emulsified starting materials are supplied in a constant amount by a metering pump to a mixing reactor. This arrangement is fundamentally a cylinder with a jacket and the interior of the cylinder (where emulsification by stirring is effected) provided with protuberant blades or scraping blades rotatable at a speed of about 100-600 r.p.m. In general, the emulsification by stirring is effectuated in the cylinder with a jacket and then the product is rapidly cooled in a cooling cylinder and is continuously discharged. Further, there is also known a system wherein starting materials are fed, without using any preliminary emulsifying tank, from the starting materials-dissolving tank directly to the body of the mixing reactor for emulsification by the aid of a metering pump and then the product rapidly is cooled in a cooling cylinder and is continuously discharged therefrom. The former is called the non-proportional system and the latter the proportional system.
It is characteristic of this apparatus that quick cooling of the product is possible and that the product can continuously be discharged. However, this apparatus has drawbacks is that cleaning of the interior of the cylinder where blades of a complicate shape are positioned becomes incomplete and that the product is rapidly cooled so that control becomes difficult in a recipe system which requires gradual cooling. In any of the non-proportional and proportional systems, the quality of the product may not be definite between the product obtained in the initial stage of the production and that in the latter stage of the production.
A continuously mixing and emulsifying apparatus having a plurality of mixing chambers is also known. Such an apparatus is disclosed in U.S. Pat. No. 3,807,703 and DOS No. 2,339,530. A mixing and emulsifying apparatus of this type relates to an apparatus developed chiefly for efficiently producing polyurethane and the like. The mechanism of the mixing and emulsification is characterized in that the mixing and emulsification are effected in an axial flow state caused by a voltex effect according to the Stokes principle by the action of a rotor shaped to have a specific element based on turbine blades or propeller blades installed in the housing and that the starting material flow in a steady flow state existing in the neighborhood of the outer layer in the housing is changed to a non-steady flow state by the action of a baffle bar thereby enhancing the mixing efficiency.
In case of manufacturing an emulsion having a very small particle size or a highly viscous emulsion (for example, a cream) or dispersion (for example, a pigment paste) of a high inner phase (the state wherein the content of a dispersion phase is greater than that of a matrix phase), however, this mixing and emulsifying apparatus has serious drawbacks as will be described hereinafter.
1. As the rotor is a one-end-supported type, its rotation becomes eccentric so that a limitation exists preventing at a high speed. Accordingly, the apparatus can be applied for an ordinary emulsion (for example, a particle size within the range of 1-100.mu., optimally 1-5.mu.) but can hardly be applied to the manufacture of an emulsion of very fine particles which requires a high speed of rotation as an indispensable condition.
2. Since the action of this mixing and emulsifying apparatus is based on mixing and emulsification by a vortex effect, it is difficult to divide particles into those of less than a certain definite size even if a high speed of rotation is possible.
3. Even if the shape of the element is changed so as to impart a shearing force, a baffle bar installed in the housing constitutes an obstacle so that a fluid boundary layer portion in the neighborhood of the outer layer in the housing forms a dead space, thus giving only an unhomogeneous and unstable emulsion. Especially, in case of the fluid starting materials having a high viscosity like an emulsion of a high inner phase type, any baffle action by a baffle bar (conversion of a steady flow into a non-steady flow) cannot be expected so that this tendency becomes more significant.
4. Emulsification proceeds in such a manner that the fluid starting materials are repeatedly passed through an orifice formed between a land and a bore always in turbulent state. Thus, the emulsion tends to become unhomogeneous, having a wide range of particle diameters. On agitation at a high speed, the fluid starting materials per se are heated. In this mixing emulsifier, however, the heat conversion rate is so poor that the emulsion tends to be denatured thermally.
Furthermore, the apparatus itself had the following problems:
1. As the rotor is of an integrated type, the rotor requires construction by a split die type and, as a result of the construction, liquid contents tend to leak out.
2. As the rotor is of a one-end-supported type, a limitation exists in the number of dispersion chambers to be installed.
3. As the mixing is fundamentally based on a vortex action, the internal pressure in the housing becomes unstable, thus making control of the flow rate difficult.
Thus, an apparatus which satisfies the following conditions is now greatly demanded in view of such prior problems:
1. An apparatus operable continuously for emulsification and dispersion and applicable to starting components an materials having a wide range of viscosities.
2. A continuous treatment is possible from charging starting materials to discharging products without the necessity of effecting any preliminary dispersion.
3. A loss of shearing energy on carrying out dispersion is so little that a significant saving of energy is possible as compared with the known conventional apparatus.
4. Energy conversion toward a fluid is made so stable that products having desired particle diameters may be obtained steadily.
5. Thermally unstable starting materials can also be processed without any problem.